As is known to those skilled in the art an orthotic is an apparatus used to support, align, prevent, or correct deformities or to improve the function of movable parts of the body. A foot orthotic can take the form of a simple metatarsal pad, a heel pad or an arch support. Arch supports are worn for comfort and for medical purposes. Arch failure or “weak arches” are known to cause a myriad of foot pathologies including bunions, hammertoes, tendon strain and ligament strain. Thus, arch supports are commonly prescribed by health professionals to treat many forms of foot pain or foot deformity.
Traditional arch supports achieve their clinical benefit by providing mechanical support to a limited area of the foot, namely the bones which comprise the medial longitudinal arch. This support is provided by a foot bed which has a raised contour which is generally shaped to conform to an “average” shape of the arch of the human foot. However, there is no universal shape of the arch of the foot of humans. The length, width and height of the arch of the human foot vary widely among all human beings.
Custom foot orthotic devices are manufactured with a goal to mold the device to the specific shape of the foot of the user. While the comfort of such a molded device is superior to a non-custom orthotic, the medical benefits of a custom foot orthotic have not been clearly demonstrated in numerous studies published in the medical literature. In fact, accurate molding of the arch of an orthotic to the foot of the user has not been shown to significantly improve alignment or prevent foot pathology. Custom orthotic devices may have benefit for reasons other than simple arch support. True functional foot orthotics correct deformities which cause the foot to compensate by rolling inward at the ankle joint (pronation) or outward (supination). Also, molding of a custom orthotic to the heel of the user, utilizing a deep heel cup is thought to improve alignment and function of the foot.
While enhancing stability of the arch of the foot is a common goal in the use of foot orthotic devices, achieving that goal is more difficult than one would expect. In this regard, the human foot has a narrow range of tolerance of pressure applied by a support to the tissues under the bone structures of the medial arch. Therefore, clinicians have looked to other methods of “indirectly” raising the arch of the foot with orthotic devices. One well accepted method is an impression casting technique where the clinician will purposefully “lock” the position of the midtarsal joint of the foot. The midtarsal joint is the primary movement interface of the bones of the arch of the foot. This joint can be aligned in more stable manner, simply by positioning certain bone segments of the foot. This is known as the “locking mechanism” of the midtarsal joint.
The locking mechanism of the midtarsal joint was originally described by H. Elftman in his article entitled “The Transverse Tarsal Joint and Its Control”, appearing in Clin. Othop 1960, 16:41-45 and that has been validated and embraced by foot health professionals for the past 60 years. It has also recently been validated by C. B. Blackwood, T. J. Yuen, B. J. Sangeorzan and W. R. Ledoux in their article entitled “The Midtarsal Joint Locking Mechanism” appearing in Foot Ankle Int. 2005, 26: 1074-1080.
As is known the locking mechanism of the midtarsal joint is accomplished by two simple movements of the bone segments which lie on either side of the midtarsal joint: (1) the rearfoot or calcaneus (heel bone) is inverted (twisted towards the midline of the body), and (2) the forefoot (metatarsals) is everted (twisted away from the midline of the body. Therefore, to “lock” the midtarsal joint of the left foot: the forefoot is twisted in a clockwise direction, while the rearfoot is twisted in a counter clockwise direction. In practice, to “lock” the midtarsal joint of the right foot, the right forefoot is twisted in a counter clockwise direction while the right rearfoot is twisted in a clockwise direction. The locking of the midtarsal joint of the left foot is accomplished by twisting the left forefoot in the clockwise direction while the left rearfoot is twisted in the counter clockwise direction. This twisting movement of two segments of the human foot has long been recognized as a motion and ultimate position of the foot which has improved stability and function. A locked and stable midtarsal joint is thought to provide more leverage for propulsion during gait.
It is also known that a locked and stable midtarsal joint will raise the arch of the foot while an unlocked midtarsal joint will lower the arch of the foot. Therefore, an indirect way to raise the arch of the foot, without actually pushing against the arch of the foot would be a mechanism which “locks” the midtarsal joint.
The locking mechanism and effects of stability on the arch of the foot was described in a different way by a noted anatomist and orthopedist, S. K. Sarrafian M.D. in his article entitled “Functional Characteristics of the Foot and Plantar Aponeurosis under Tibiotalar Loading”, appearing in Foot Ankle 8: 4-17, 1987. In that article Dr. Sarrafian observed that the human foot was constructed like a “twisted plate” whereby the bones of the rearfoot (i.e., talus and calcaneus) were oriented in a vertical alignment, while the bones of the forefoot were oriented in a horizontal alignment. Dr. Sarrafian also noted that when the twisted plate arrangement of the bones of the foot was further twisted, i.e., the forefoot was twisted in an everted direction while the rearfoot was twisted in an inverted direction the height of the arch of the foot was raised while the length of the arch was shortened.
Compared to primates, the human foot has bones in this twisted plate alignment which allows the formation of the medial and lateral arches, and allows the mechanical stability of the human foot which is not found in any other animal population.
Whether the bones of the human foot are moved in a way to lock the midtarsal joint, or to “twist the plate” the force or movement applied against the forefoot and rearfoot are the same: the forefoot is twisted in an everted direction, while the rearfoot is twisted in an inverted direction. The end result is a more stable foot structure which has less of a load on the passive soft tissues which normally support the arch.
While knowledge of the osseous locking mechanism of the human foot and the “twisted plate” phenomenon of the raising of the height of the arch has been known and published for at least 20 years, there has been no technology developed which would position the foot according to these principles. Specifically, there has been no foot orthotic device designed to twist the bone structure of the human foot in such a way to indirectly raise the height of the medial longitudinal arch and lock the midtarsal joint for stability.
In an article by Kogler G F, Veer F B, Solomonidis S E, Paul J P entitled: “The influence of medial and lateral placement of orthotic wedges on loading of the plantar aponeurosis”, Journal of Bone and Joint Surgery 81-A: 1403, 1999, a forefoot lateral wedge was used in a study to measure strain in the plantar aponeurosis, which is a primary ligament which supports the arch. The wedge was described as being commonly used clinically and had an angle of 6 degrees and a thickness of 5, 6 or 7 mm. The wedge was placed starting at mid-shaft of the metatarsals and extended all the way to the end of the toes. The authors reference a locking effect of the wedge solely to the calcaeal-cuboid joint (which is one of two joints in the midtarsal joint) and do not reference a change of arch height. Their primary conclusion is about relieving strain in the plantar aponeurosis.
Thus, a need exists for a device which can be incorporated into an article of footwear for indirectly raising the arch of the wearer's foot by locking the midtarsal joint. The subject invention addresses that need and is arranged to be incorporated in any type of footwear, e.g., shoe, sandal, etc.
All references cited herein are incorporated herein by reference in their entireties.